Simple surrogate models to determine total accessibility duration of low Earth orbit sunsynchronous satellites

Abstract

Short and infrequent access events are inherent characteristics of low Earth orbit sunsynchronous satellites. Furthermore, for such satellites, distribution pattern of access events varies significantly in time. Thus, determination of the metric of total accessibility duration in a given time interval has been a challenge in the field of low Earth orbit satellite systems engineering. In this article, for zero and conventional non-zero minimum elevation angles, surrogate models were developed to determine total accessibility duration of low Earth orbit satellites, based on orbital altitude of the satellite and latitude of the ground segment. For this purpose, concept of repeatability cycle was employed to achieve total accessibility duration in a time-independent manner. Then, a perturbative propagation model was presented to determine pattern of accessibility events and quantify total accessibility duration metric. In order to account for non-zero minimum elevation angles, two distinct approaches were adopted. In the first approach, four modification factors were introduced to modify the surrogate model for zero elevation angle to account for conventional non-zero minimum elevation angles. In the second approach, a dedicated surrogate model was developed to directly determine total accessibility duration for conventional non-zero minimum elevation angles. Numerous examples are examined to verify fidelity of our two proposed approaches. Due to their simplicity, the surrogate models given in this article eliminate the need for professional staff to determine metric of total accessibility duration. The advantage is that considerable saving in required initial staff cost and schedule can be realized, especially in early mission design phases.